Crystal structures of the sulfones of 2,3-diphenyl-2,3-dihydro-4H-1,3-benzothiazin-4-one and 2,3-diphenyl-2,3-dihydro-4H-pyrido[3,2-e][1,3]thiazin-4-one

The title sulfones crystallize in space group P21/n with two molecules in each of the asymmetric units and have almost identical unit cells and extended structures. In both structures, the thiazine rings exhibit a screw-boat pucker.


Structural commentary
The two title compounds (Figs. 1 and 2) are structurally very similar with two molecules of each in the asymmetric units of the respective crystals. Both of the crystal structures are in the monoclinic space group P2 1 /n with very similar unit-cell dimensions, and are fairly well superimposable (Fig. 3).
The structures of 1 and 2 both display a screw-boat (pucker) conformation for the four thiazine rings in the two asymmetric units [puckering amplitude Q ranging between 0.616 (4) and 0.6449 (16) Å , and the and ' values, after accounting for the absolute conformation transformations, are between 60.7 (4) and 63.02 (16) , and 140.53 (18) and 142.9 (4) , respectively]. The puckering observed is similar to that in the sulfoxides 5 and 6 (Yennawar, Fox et al. 2017;Yennawar, Noble et al. 2017), but is different from the envelope conformations seen in the sulfides 3 and 4 (Yennawar, Bendinsky et al., 2014;Yennawar, Singh et al., 2014). Each molecule contains one stereogenic center, which lies between the N atom and the SO 2 group of the heterocyclic ring: in the asymmetric unit of 1, C8 has an S configuration and C28 an R configuration, thus generating a racemic pair. The situation is 2 is similar, with C8 S and C28 R.
In compound 1, the dihedral angle between the substituent phenyl rings is 58.7 (2) and 57.4 (3) in the two asymmetric molecules. Between the co-planar atoms of the fused benzene and the phenyl rings, the dihedral angle ranges between 83 and 100 . Compound 2 is again similar, showing a dihedral angle between the substituent phenyl rings of 53.04 (11) and 57.24 (13) . Between the co-planar atoms of the pyridine ring and the phenyl rings of the respective structures, the dihedral angle ranges between 76 and 101 .

Supramolecular features
Both of the extended structures are consolidated by C-HÁ Á ÁO hydrogen bonds (Tables 1 and 2). Assuming that the C-HÁ Á ÁO angle should be greater than or equal to 130 as one of the qualifiers for such interactions, a very small variation in molecular positioning in the two structures results in The asymmetric unit of 1 with displacement ellipsoids drawn at 50% probability level.

Figure 2
The asymmetric unit of 2 with displacement ellipsoids drawn at 50% probability level.

Figure 3
Overlay plot of 1 and 2 where atoms S1 and S2 of the two structures are matched. The atoms that differ in the two structures, namely C2 and C22 of 1 and N2 and N4 of 2, are labeled. two additional interactions for 2 as compared to that in 1. However, in both structures (starting from the interactions within the asymmetric units followed by translation periodicity along the a direction) intermolecularstacking interactions between the fused aromatic rings, namely the benzene ring of the benzothiazine unit in 1 and the pyridine ring of the pyridothiazine unit in 2, can be seen (Figs. 4 and 5). The centroid-centroid separations in 1 are 3.522 (3) and 3.521 (3) Å with corresponding values of 3.5715 (15) and 3.5991 (15) Å in 2.

Synthesis and crystallization
TLC plates (silica gel GF, 250-micron, 10 Â 20 cm, cat. No. 21521) were purchased from Analtech. TLCs were visualized under short-wave UV, and then with I 2 , and then by spraying with ceric ammonium nitrate/sulfuric acid and heating.
Infrared spectra were run on a Thermo-Fisher NICOLET iS50 FT-IR using a diamond-ATR attachment for direct powder analysis (Penn State Schuylkill). 1 H and 13 C NMR experiments (Penn State's shared NMR facility, University Park) were carried out on a Bruker Advance-III-HD 500.20-MHz ( 1 H frequency) instrument using a 5 mm Prodigy (liquid nitrogen cooled) BBO BB-1H/19F/D Z-GRD cryoprobe. Samples were dissolved in CDCl 3 and analyzed at room temperature. Typical conditions for 1 H acquisition were 2 s relaxation delay, acquisition time of 4.089 s, spectral width of 8 kHz, 16 scans. Spectra were zero-filled to 128k points, and multiplied by exponential multiplication (EM with LB = 0.3 Hz) prior to FT. For the 13 C experiments, data were acquired with power-gated 1 H decoupling using a 2 s relaxation delay, with acquisition time of 1.1 s, spectral width of 29.8 kHz, and 256 scans. Spectra were zero-filled once, and multiplied by EM with LB = 2 Hz prior to FT. The exact masses of the synthesized compounds were determined using LC-MS (Villanova University). Exact mass was measured on a SCIEX Exion LC with a SCIEX 5600+ TripleTOF MS. Separation was achieved on an Agilent Infinity LabPoroshell 120 EC-C18 column maintained at 40 C with a gradient of 90/ 10 (water/acetonitrile with 0.1% formic acid) ramped from 5/ 95 over 6 min at a flowrate of 0.5 ml min À1 . The TOF-MS was scanned over 100-500 Da and calibrated with the SCIEX APCI positive calibrant solution prior to accurate mass analysis. Compound exact mass was measured in positive ESI  Crystal packing diagram for 1 showing intermolecular pairs of C-HÁ Á ÁO hydrogen bonds. Columns (four per unit cell) of molecules with alternating chirality, due to the translational periodicity down the a direction can be envisioned.
mode with a DP = 100 V, CE = 10, GAS1 = GAS2 = 60 psi, CUR = 30 psi, ISV = 5500 V, and source temperature of 450 C. Melting points were performed on a Vernier Melt Station (Penn State Schuylkill). General Oxidation Procedure (Surrey et al., 1958;Silverberg, 2020;Cannon et al., 2015): The heterocycle (0.267 mmol) was dissolved in glacial acetic acid (1.2 ml). An aqueous solution of KMnO 4 (0.535 mmol in 1.45 ml water) was added dropwise at room temperature with vigorous stirring. The reaction was followed by TLC. Solid sodium bisulfite (NaHSO 3 /Na 2 S 2 O 5 ) was added until the solution remained colorless; 1.45 ml of water was added and stirred for 10 min. The mixture was extracted with CH 2 Cl 2 (3 Â 5 ml). The organics were combined and washed once with sat. NaCl. The solution was dried over Na 2 SO 4 and filtered. The product was purified by chromatography in a silica gel micro-column with mixtures of ethyl acetate and hexanes. Crystals for X-ray were grown as detailed below.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The hydrogen atoms were placed in their geometrically calculated positions and refined using the riding model with parent-atom-H lengths of 0.93-0.95 Å (aromatic CH) and 0.98-1.00 Å (methine CH). Isotropic displacement parameters for these atoms were set to 1.2 times U eq of the parent atom.

Funding information
Research reported here was conducted on instrumentation funded by National Science Foundation: CHEM-0131112 for the Bruker AXS diffractometer, and SIG S10 grants of the

Special details
Experimental. The data collection nominally covered a full sphere of reciprocal space by a combination of 4 sets of ω scans each set at different φ and/or 2θ angles and each scan (10 s exposure) covering -0.300° degrees in ω. The crystal to detector distance was 5.82 cm. Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.